光子晶体光纤非线性系数的数值计算

针对全反射型光子晶体光纤在短波长处的横向电场分布特点，在忽略空气孔内极为微小的电场影响下，将光纤等效为阶跃型光纤，导出一种新的计算有效折射率的方法.结合Sellmeier公式推出光子晶体光纤的非线性系数与其两个几何结构参量和波长的简洁解析关系.对非线性系数随着这些参量的变化进行了数值计算与讨论，得出非线性随着空气孔直径或空气孔直径与孔间距比d/Λ值的增大成指数上升的规律.在波长为0.55 μm和0.85 μm时，非线性系数分别可高达3.5和2.54 m－1W－1.

Numerical Calculations of Nonlinear Coefficient of Photonic Crystal Fibers

According to distribution characteristics of the transverse electronic field in total internal reflection (TIR) photonic crystal fiber (PCF), a new approach to calculate the effective index is employed with neglecting the small fraction of the electrical power residing in the air-hole regions and regarding TIR PCF as an equivalent step-index fiber. Using Sellmeier equation, a simple expression of the nonlinear coefficient is derived as a function of two geometric structure parameters and light wavelength. And, the changes of the nonlinear coefficient under different parameters are calculated and discussed. It is found that nonlinear coefficient increase exponentially with the increase of air-hole diameter and its ratio to the pitch. In particular, the maximum values of nonlinear coefficient can reach 3.5 and 2.54 m-1W-1 for 0.55 μm and 0.85 μm wavelength respectively.